Evaporation of polar stratospheric cloud particles, in situ, in a heated inlet

Trude Eidhammer, University of Wyoming

In December 2001 and 2002 in situ aerosol measurements were made from balloon-borne platforms within polar stratospheric clouds (PSC) consisting of supercooled ternary solutions, nitric acid trihydrate and ice. Particle size (radius > 0.15 micrometer) and number concentrations were measured with two optical particle counters. One of these included an 80 cm inlet heated to > 245 K.

The heated inlet was used to obtain a measurement, within a PSC, of the size distribution of the background stratospheric particles upon which the PSC particles condensed. The measurements are compared to models that calculate the evaporation of PSC particles. The modeled evaporation for supercooled ternary solutions is in good agreement with the measurements.

For the nitric acid trihydrate it is uncertain what happens to the particle as it is brought to temperatures much higher than its equilibrium temperature at stratospheric temperatures and partial pressures. Here the modeled evaporation show too low evaporation compared to the measurements.